Extensions of previous work and new projects are proposed in the following areas: (1) Studies on proinsulin and the biosynthesis of insulin, including studies on human proinsulin, studies on the mechanism of peptide chain "folding" and disulfide bond formation in proinsulins from various species, further efforts to localize and characterize the proteolytic enzymes involved in the conversion of proinsulin to insulin, and comparative studies of proinsulin and insulin structure in primitive vertebrates and invertebrates. (2) Studies on isolated beta cells and beta cell plasma membranes. Efforts will be made to develop methods for large scale isolation of islets for these and related studies. Isolated beta cells and beta cell membranes will be characterized with emphasis on regulatory aspects, i.e., surface proteins and receptors, enzymes such as adenyl cyclase, and glycoproteins. (3) Studies on the biosynthesis of insulin and glucagon in beta cell tumors from rats injected with nicotinamide and streptozotocin. Tissue culture experiments will be conducted using tumors and normal islets to obtain insulin- or glucagon-producing cell lines. (4) Studies on insulin binding, degradation, and biological activity in normal and diabetic liver. These studies will utilize whole animal experiments, isolated perfused livers and isolated hepatic parenchymal cells to study the correlation between the binding of insulin and its degradation, and the molecular consequences of insulin binding at the liver plasma cell membrane. The mechanism of stimulation of glycogen synthesis by insulin will be examined in detail, both in isolated liver cells and in cell-free systems. An important goal of these experiments will be to identify the intracellular effector(s) which mediate the action of insulin.